Delay line interferometers are typically Mach-Zehnder type or Michelson type interferometers based on multiple beam interference in which one beam is time-delayed to another by a desired interval. As applied to Differential Phase-Shift Keying (DPSK), demodulation delay line interferometers convert a phase-keyed signal into an amplitude-keyed signal. In this application, an incoming DPSK optical signal is split into two equal-intensity beams in two arms of a interferometer, wherein one beam is delayed by a given optical path difference corresponding to a one bit delay in the DPSK scheme. The beams are recombined producing constructive or destructive interference in the time domain for each bit. The resultant interference intensity is the intensity-keyed signal.
Delay line interferometers for DPSK systems are high performance optical devices requiring precision optical components, frequently with costly optical coatings. Simplifying the construction of DPSK demodulators without compromising performance would represent an important advance in the technology.